Timing synchronization for image scanning

Abstract

A scanner has a window in its housing through which the scanning beam emerges to impinge upon an indicia to be read. The window is elongate, and adjacent each end, on the inside of the housing, there is a bar code symbol structure. In use, the scanning beam first scans across the symbol structure at one end of the window, then passes through the window to impinge upon the indicia, then scans across the second symbol structure at the other end of the window. Reflected light from the two code symbol structures and from the indicia, are received by a photodetector. The reflected light from the bar code symbol structures on the inside surface of the housing provides locating and timing information which enables the scanner to produce an accurate special reconstruction, in computer memory, of the indicia. In an alternative embodiment, the beam moves in a raster pattern, and there is a further locating/timing/synchronization bar code symbol structure adjacent a long edge of the window. At least one of the raster lines passes over this bar code symbol structure, thereby obtaining further locating and timing information.

We claim: 
     
       1. A scanner for reading indicia comprising: (a) scanning means for scanning a light beam over a predetermined area, said area covering an indicia to be read;   (b) masking means positioned in the beam intermediate the scanning means and the indicia, and out of the plane of the indicia, the masking means carrying at least one coded symbol; and   (c) means for receiving light reflected from the indicia and for reading the indicia using information from the at least one coded symbol.   
     
     
       2. A scanner as claimed in claim 1 wherein the at least one coded symbol comprises at least one bar code symbol. 
     
     
       3. A scanner as claimed in claim 1 wherein the at least one coded symbol comprises a timing code. 
     
     
       4. A scanner as claimed in claim 3 wherein the at least one coded symbol comprises a speed compensation grating. 
     
     
       5. A scanner as claimed in claim 1 wherein the at least one coded symbol comprises a first code portion to one side of the indicia and a second code portion to an opposite side of the indicia, whereby the beam scans first across the first code portion, then across the indicia, then across the second code portion. 
     
     
       6. A scanner as claimed in claim 5 wherein at least one of the first and second code portions comprises a guard bar. 
     
     
       7. A scanner as claimed in claim 1 wherein the scanning means produces a raster scan, the at least one coded symbol comprising an elongate code symbol structure which is scanned by one or more raster lines before subsequent raster lines scan across the indicia. 
     
     
       8. A scanner as claimed in claim 7 wherein the at least one coded symbol further includes a first code symbol structure to one side of the indicia and a second code symbol structure to an opposite side of the indicia, whereby at least one line of the raster scan scans the elongate code symbol structure, and at least one subsequent line of the raster scan scans first across the first code symbol structure, then across the indicia, then across the second code symbol structure. 
     
     
       9. A scanner as claimed in claim 8 wherein a further elongate code symbol structure is provided on an opposite side of the indicia from the said elongate code symbol structure, at least one raster scan line being arranged to scan across said further elongate code symbol structure after the indicia has been scanned. 
     
     
       10. A scanner as claimed in claim 8 wherein the first and second code symbol structures comprise guard bars and the elongate code symbol structure comprises a speed compensation grating. 
     
     
       11. A scanner as claimed in claim 1 having a housing and a window in the housing through which the beam passes to impinge upon the indicia, the masking means comprising those parts of the housing which define the window, and the at least one coded symbol being located on a surface of the housing adjacent to the window. 
     
     
       12. A scanner as claimed in claim 11 wherein the window is generally rectangular and is defined by an upper edge, a lower edge, a first side edge and a second side edge, the beam scanning across the window from the first side edge to the second side edge, and the at least one coded symbol comprises a first code portion adjacent the first side edge and a second code portion adjacent the second side edge. 
     
     
       13. A scanner as claimed in claim 11 wherein the window is generally rectangular and is defined by an upper edge, a lower edge, a first side edge and a second side edge, the beam scanning in a raster fashion in a series of generally parallel lines, the at least one coded symbol comprising an elongate code symbol structure adjacent the upper edge of the window, a first code portion adjacent the first side edge and a second code portion adjacent the second side edge, wherein at least one raster line scans across the elongate code symbol structure, and at least one subsequent raster line scans first across the first code portion, then across the window, and then across the second code portion. 
     
     
       14. A scanner as claimed in claim 13 wherein the first and second code symbol structures comprise guard bars and the elongate code symbol structure comprises a speed compensation grating. 
     
     
       15. A scanner as claimed in claim 14 wherein a further elongate code symbol structure is provided adjacent the lower edge of the window, at least one raster line scanning across said further elongate code symbol structure after said window has been scanned. 
     
     
       16. A scanner as claimed in claim 11 in which the window is generally rectangular and is defined by an upper edge, a lower edge, a first side and a second side edge, the beam scanning in a raster fashion in a series of generally parallel lines, the at least one coded symbol comprising an elongate code symbol structure adjacent the upper edge of the window, the elongate code symbol structure being read by one or more raster lines before subsequent raster lines scan across the window. 
     
     
       17. A scanner as claimed in claim 1 wherein the means for reading the indicia uses light reflected from the at least one coded symbol. 
     
     
       18. A scanner for reading indicia comprising: (a) scanning means for scanning a light beam over a predetermined area, said area covering an indicia to be read;   (b) masking means positioned in the beam intermediate the scanning means and the indicia, and out of the plane of the indicia, the masking means carrying at least one CCD; and   (c) means for receiving light reflected from the indicia and for reading the indicia using information from the at least one CCD.   
     
     
       19. A scanner as claimed in claim 18 wherein the CCD is arranged to produce an electrical signal, said electrical signal providing information which is used to read the indicia. 
     
     
       20. A method of reading indicia comprising: (a) scanning a light beam over a predetermined area, said area covering an indicia to be read;   (b) positioning masking means in the beam intermediate the scanning means and the indicia, the masking means being out of the plane of the indicia, and the masking means carrying at least one coded symbol; and   (c) receiving light reflected from the indicia and reading the indicia using information from the at least one coded symbol.   
     
     
       21. A scanner as claimed in claim 11 wherein the window is generally rectangular and is defined by an upper edge, a lower edge, a first side edge and a second side edge, the beam scanning at least between said upper edge and one of said side edges or between said lower edge and one of said side edges.